In various molding/forming machines such as an injection molding machine and a press-forming machine, and a machining device (machining machines) such as a bonding machine, an electrically-powered mechanism (mechanical driving unit) is driven by a motor, thereby applying a pressure on a pressurized target. Moreover, in those machining devices, generally, an actual pressure value, which is pressure information when the mechanical load is pressed against a material to be molded/formed or the like or a workpiece, which is the pressurized target, is detected, and pressure control is performed based on the detected actual pressure value and a pressure command value. Based on this pressure control, a current command value, a speed command value, and the like, which are signals for controlling the motor, are calculated so that the actual pressure value follows the pressure command value.
One example of the calculation for the pressure control is calculation of a speed of a motor based on a speed command value calculated by multiplying a deviation (difference) between a pressure command value and the actual pressure value by a proportional gain. In general, by setting the gain characteristic of the calculation for the pressure control to a relatively large value, a capability of the actual pressure value to follow the pressure command value can be improved. On the other hand, when the proportional gain is set to an excessively large value, stability of a control system is compromised, the control system becomes unstable, and an oscillation phenomenon in which a high frequency vibration is superimposed on a pressure applied to a pressurized target occurs.
Needless to say, it is not preferred that the control system become unstable, and an adverse effect is generated on formed/molded products and machined products by the generated oscillation phenomenon. On the other hand, the oscillation phenomenon is prevented by setting the gain characteristic to a relatively small value but a characteristic of an actual pressure value to follow a pressure command value decreases. This leads to an error of the actual pressure value, which is a pressure actually applied, with respect to the pressure command value, which is a desired pressure, resulting in a problem in that an adverse effect is generated on forming/molding precisions of the formed/molded products and a machining precision of the machined products.
In order to address this problem, for example, in a conventional device described in Patent Literature 1, a die cushion control device produces a correction value, which is a product of a derivative of a pressure command value and a coefficient, and adds the correction value to a speed command value, thereby improving the capability of an actual pressure value to follow the pressure command value.